Apparatus for vehicle direction sensing

ABSTRACT

The direction of travel of a vehicle is determined by mounting four electrical strain gage elements at the four corners of a rectangular shaped platform and by interconnecting the same in a bridge circuit arrangement such that an output of a given polarity will be developed as the vehicle traverses a leading portion of the platform and an output of a different polarity will be developed as the vehicle traverses the trailing portion of the platform.

United States Patent Inventor Olul Olsen Manchester, Mass.

Appl. No 881,999

Filed Dec. 4, 1969 Patented July l3, I971 Assignee IlLll Electronics,Inc.

Wlltlurn, Mm

APPARATUS FOR VEHICLE DIRECTION SENSING 9 Claims, 3 Drawing Figs.

us.c|. 340/39.

111/134 m.c1 cos; 1/02 rim of swat v. 340/39;

177/132, 133, I34, I36, l63,2l0, 211

DIRECTION OF TRAVEL [56] References Cited UNITED STATES PATENTS3,533,481 10/1970 Paelian. .1 177/134 Primary Examiner--Kathleen l-l.Clalfy Assistant Examiner-Randall P Myers Au0mey.r-.lames E Mroee andMary C. Thompson ABSTRACT: The direction of travel of a vehicle isdetermined by mounting four electrical strain gage elements at the fourcorners of a rectangular shaped platform and by interconnecting the samein a bridge circuit arrangement such that an output of a given polaritywill be developed as the vehicle traversea a leading portion of theplatform and an output of a different polarity will be developed as thevehicle traverses the trailing portion of the platform.

ATENIEU JUL 1 31971 DIRECTION OF TRAVEL FIG 2 VOLTS INV ENTOI OLUF OLSENDISTANCE OW) Mish ATTUIIN E15 APPARATUS FOR VEHICLE DIRECTION SENSINGBACKGROUND OF THE INVENTION The present invention relates generally tovehicle direction sensing and in one particular aspect, to uniqueapparatus for sensing the direction of travel of a moving vehiclethrough the use of electrical strain gage responsive elements, theunique apparatus being particularly well suited for use with treadletype weighing scales.

Many application exist where it is desirable to be able to sense thedirection of travel of a moving vehicle. For example, in toll booths, atreadle type weighing system maybe used to digitally record the weightof each axle approaching the booth so that an accurate charge can bemade. In such toll booth weighing systems it would be undesirable tohave weight recorded on a vehicle which, for some reason, traversed thescales in the reverse direction in that an inaccuram toll charge wouldbe made due to a double recording of a particular axle weight.

Another exemplary application for the use of vehicle direction sensingis in the counting of the number of vehicles passing down a particularstreet, crossing a bridge or the like. Such a count is important inenabling a proper determination to be made of the timing sequence forlights at an intersection, to determine whether a street needs to bewidened to accommodate more vehicles, or to determine whether additionalbridges or the like are needed. In determining such counts, it isimportant that the same vehicle be counted only once so that a propervehicle count is obtained.

In the past, the sensing of direction of travel of a vehicle wasobtained by the placing of four pairs of metal strips or pressuresensitive gages beneath a rubber pad or mat. The pairs of metal stripsor pressure sensitive gages would be mounted such that upon the passingof a vehicle thereacross respective relays would be energized. Byobserving the sequence of relay energization, as a vehicle passed acrossthe sensing devices, the direction of travel of the vehicle would beobtained. While somewhat satisfactory, one problem with theabove-described direction sensing arrangements was that the rubber padsor mats were subject to rapid wear and would, in face, crack. Thecracking would have the disadvantageous effect of allowing both dirt andwater to get into the sensing devices and thereby destroy both theirreliability and use. Moreover, the prior art type direction sensingarrangements lacked precision measurement and were difi'icult toinstall.

SUMMARY OF THE INVENTION Accordingly, one object of the presentinvention is the provision of unique apparatus for vehicle directionsensing.

Another object of this invention is to provide a novel and improvedapparatus which includes electrical strain gage elements for sensing thedirection of travel of a vehicle.

Still another object of this invention is to provide a novel andimproved apparatus for sensing the direction of travel of a vehiclewhich is particularly well suited for use in conjunction with a treadlescale type system such that the true weight of a vehicle may be realizedregardless of its direction of travel.

One other object of the subject invention is to provide a unique vehicledirection sensing appamtus which includes a platform having electricalstrain responsive elements mounted thereon and connected in a circuitarrangement such that the direction of travel of a vehicle may bedetermined by examining the polarity of the output of the circuitarrangement.

In one practice of these teachings a substantially rigid platformstructure of relatively broad area and having a leading portion and atrailing portion includes a plurality of electrical strain responsiveelements mounted in the separate corners thereof and connected in abridge circuit arrangement such that different polarity output voltageswill be generated depending upon which portion along the platform thevehicle is traversing.

BRIEF DESCRIPTION OF THE DRAWINGS Although the features of thisinvention considered to be novel are expressed in the appended claims,further details as to preferred practices and as to the further objectsand features thereof may be most readily comprehended through referenceto the following description taken in connection with accompanyingdrawings, wherein:

FIG. 1 portrays a preferred embodiment of the positioning of electricalstrain gage responsive elements upon a platform used for vehicledirection sensing according to the present invention;

FIG. 2 illustrates a bridge circuit arrangement connecting theelectrical strain gage responsive elements of the subject invention insuch a fashion as to sense the direction of travel of a moving vehicle;and,

FIG. 3 is a graph showing typical output voltage curves for a vehicle asit traverses the platform of the subject invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to thedrawings wherein like reference numerals designate identical, orcorresponding parts throughout the several views, and more particularlyto FIG. I thereof wherein is portrayed a substantially rigid platformIII of a relatively broad area and having electrical strain gagesmounted thereupon in a unique fashion for sensing the direction oftravel of a vehicle approaching in a direction indicated by the arrow12. The platform 10 is generally of rectangular shape and is shown ashaving a leading portion I4 and a trailing portion 16. The electricalstrain gages 20, 22, 24 and 26 may be of the wire, foil or semiconductortypes and are mounted in the four separate corners of the platformstructure I0. Additionally, the electrical strain gages 20, 22, 14 and26 are positioned in such a direction as to be in tension or compressionupon the deformation of the platform structure 10 due to the applicationof a load thereto depending upon gage placement. It can be seen that asa vehicle approaches the leading portion I4 of the platform 10, theelectrical strain gages 20 and 24 will experience a greater force intension than that of the strain gages 22 and 26 due to a greaterdeformation in the portion of the platform to which the vehicle isapplied. Likewise, as the vehicle moves into the trailing portion [6 ofthe platform 10 the electrical strain gages 22 and 26 will experience agreater tension than that of strain gages m and 24. At some place at thecenter of the platform 10, a vehicle crossing that point will cause anequal force in tension to be applied to each of the four electricalstrain gages 20, 22, 24 and 26.

Referring now to FIG. 2, a bridge circuit arrangement is thereindisclosed for interconnecting the strain gage elements of FIG. I in sucha fashion as to sense the direction of travel of a moving vehicle. Inparticular, a DC source of excitation voltage 28 is applied to theterminal points 30 and 32 to thereby apply the same across seriallyconnected electrical strain gages 20 and 22 and serially connectedelectrical strain gages 26 and 14. The output from the bridge circuitarrangement is taken across terminal points 34 and 36 and is applied toa conventional DC difi'erential amplifier 38, the function of which isto amplify the voltage appearing across the terminals 34 and 36 and togive a differential reading thereof at output terminals 40 and 42. Withthe bridge circuit arrangement as shown, a vehicle load passing exactlyat the center of the rectangular platform ll) of FIG. I will cause equalstrain output from each of the four gages 20, 22, 24 and 26 with a netaero output voltage for a given bridge excitation. If the vehicle loadwere now placed at the leading portion 14 of the platform 10, theopposite arm gages 10 and 24 will sense more strain in tension than thegages 22 and 26 on the trailing portion of the platform 10 and an outputof a given polarity will appear at terminals 40 and 42. Conversely, asthe vehicle load is moved to the trailing portion 16 of the bridge, theopposite arm gages 22 and 26 will sense more in tension strain than thegages 20 and 24 and the output signal at terminals 40 and 42 will nowreverse in polarity. This effect can be clearly seen in reference toFIG. 3 wherein typical output curves for three different weight vehicleloads I, 2 and 3 shown. For example, the curves of FIG. 3 show that as avehicle passes the leading edge portion l4 of the platform 10, namely,from to (x/2) inches (where x is the width of the platform and may betypically inches), the output voltage appearing at terminals 40 and 42will be positive and peak when the gages and 24 are in greatest tensionand will be zero as the vehicle passes the center of the platform andpeak negatively when the gages 22 and 26 are in greatest tension. Itshould be understood that the output of the leading portion 14 couldequally have been chosen to be negative, while that of the trailingportion 16 being chosen to be positive.

In addition, it should be noted that of the three different weightvehicle load indicating curves 1, 2 and 3, the number three curverepresents the heaviest load and the number one curve is the lightest.

It should also be understood that conventional output logic circuitrycould be connected to the output terminals 40 and 42 to sense thepolarity of voltage appearing thereacross and thereby indicate theparticular location of a vehicle traveling across the platform 10 at anygiven time. Such logic circuitry could include voltage comparators orother conventional threshold type devices. Additional conventional logicgating circuitry could be used to indicate the sequence of polaritychanges, for example positive to negative, and thereby indicate whetherthe vehicle is traversing in a forward or reverse direction so as toavoid a double weight measurement or count which could produce error.

In one particularly well suited application for the subject invention,the platform 10 may be a treadle scale, such as the type disclosed incopending application Scr. No. 682,278, filed Nov. l3, I967, now U.S.Pat. No. 3,474,857 issued on Oct. 28, I969 and entitled Strain-GagedTreadle Scales," by Eric Laimins, which are typically used to measureaxle weights in toll booths or the like. Thus, with the subjectinvention, if a vehicle being weighed should reverse direction duringthe weighing procedure, this will be immediately sensed so that acorrection for the same may be automatically obtained.

It should now be apparent that the apparatus of the herein describedinvention allows for the reliable indication of the direction of travelof a vehicle that is both easy to install and is of long life.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. For example, theplatform 10 of the subject invention may be either portable or fixedlysecured to a road. Additionally, it should be understood that two ormore similar type platforms may be placed in a side-byqide relation sothat both of the axles of a vehicle may be simultaneously weighed andthe direction thereof sensed. Furthermore, while the platform of thesubject invention has been shown as being preferably of rectangularshape and having four electrical strain gages posi tioned at the fourcorners thereof, the invention is not so limited and would operate withtwo strain gage elements and with platforms of differing shapes. [t istherefore to be understood that within the scope of the appended claimsthe invention may be practiced otherwise than as specifically describedherein.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. Apparatus for sensing the direction of travel of a vehicle comprisinga substantially rigid platform structure of relatively broad area andhaving a leading portion and a trailing portion, at least a firstelectrical strain gage means mounted upon the leading portion of saidplatform structure and responsive to deformations induced upon saidleading portion upon the spplication of a vehicle load thereto, at leasta second electrical strain gage means mounted upon the trailing portionof said platform structure and responsive to deformations induced uponsaid trailing portion upon the application of a vehicle load thereto,and an electrical brid e circuit arrangement having an output therefromand inc uding said first electrical strain gage means and said secondelectrical strain gage means connected in a pair of arms thereof in sucha fashion that means connected to the output of said bridge circuitarrangement will provide an output of a first polarity upon said vehicleload passing said leading portion of said platform and an output of asecond polarity upon said vehicle load passing said trailing portion ofsaid platform whereby the direction of travel of said vehicle may bereadily determined.

2. Apparatus for sensing the direction of travel of a vehicle as inclaim 1, wherein said bridge circuit arrangement is energized by asource of DC voltage which is connected across said first electricalstrain gage means and said second electrical strain gage means which areserially connected in said pair of arms.

3. Apparatus for sensing the direction of travel of a vehicle as inclaim 2, wherein is included a third electrical strain gage meansmounted upon the leading portion of said platform structure andresponsive to deformations induced upon said leading portion upon theapplication of a vehicle load thereto and a fourth electrical straingage means mounted upon the trailing portion of said platform structureand responsive to deformations induced upon said trailing portion uponthe application of a vehicle load thereto, said third electrical straingage means and said fourth electrical strain gage means being connectedin a pair of arms of said bridge circuit arrangement differing from thatof the pair of arms of said first electrical strain gage means and saidsecond electrical strain gage means.

4. Apparatus for sensing the direction of travel of a vehicle as inclaim 3, wherein said first electrical strain gage means and said thirdelectrical strain gage means are connected in opposite arms of saidbridge circuit arrangement and wherein said second electrical straingage means and said fourth electrical strain gage means are connected ina different pair of opposite arms of said bridge circuit arrangement.

5. Apparatus for sensing the direction of travel of a vehicle as inclaim 4, wherein said means connected to the output of said bridgecircuit arrangement is a DC differential amplifier, the output of saidbridge circuit arrangement being taken across the tenninal point joiningsaid first electrical strain gage means and said second electricalstrain gage means and the terminal point joining said third electricalstrain gage means and said fourth electrical strain gage means.

6. Apparatus for sensing the direction of travel of a vehicle as inclaim 5, wherein said first, second, third and fourth electrical straingage elements are of the tension or compression responsive type.

7. Apparatus for sensing the direction of travel of a vehicle as inclaim 6, wherein said platform is of substantially rectangular shape andwherein said first, second, third, and fourth electrical strain gageelements are each positioned near a different comer of said platform.

8. Apparatus for sensing the direction of travel of a vehicle as inclaim 7, wherein the output of said DC differential amplifier will bezero when the vehicle load is at the center of said platform.

9. Apparatus for sensing the direction of travel of a vehicle as inclaim 8, wherein said platform is a treadle scale used to measure theaxle weight of a vehicle as it passes thereacross without error due tovehicle direction changes.

1. Apparatus for sensing the direction of travel of a vehicle comprisinga substantially rigid platform structure of relatively broad area andhaving a leading portion and a trailing portion, at least a firstelectrical strain gage means mounted upon the leading portion of saidplatform structure and responsive to deformations induced upon saidleading portion upon the application of a vehicle load thereto, at leasta second electrical strain gage means mounted upon the trailing portionof said platform structure and responsive to deformations induced uponsaid trailing portion upon the application of a vehicle load thereto,and an electrical bridge circuit arrangement having an output therefromand including said first electrical strain gage means and said secondelectrical strain gage means connected in a pair of arms thereof in sucha fashion that means connected to the output of said bridge circuitarrangement will provide an output of a first polarity upon said vehicleload passing said leading portion of said platform and an output of asecond polarity upon said vehicle load passing said trailing portion ofsaid platform whereby the direction of travel of said vehicle may bereadily determined.
 2. Apparatus for sensing the direction of travel ofa vehicle as in claim 1, wherein said bridge circuit arrangement isenergized by a source of DC voltage which is connected across said firstelectrical strain gage means and said second electrical strain gagemeans which are serially connected in said pair of arms.
 3. Apparatusfor sensing the direction of travel of a vehicle as in claim 2, whereinis included a third electrical strain gage means mounted upon theleading portion of said platform structure and responsive todeformations induced upon said leading portion upon the application of avehicle load thereto and a fourth electrical strain gage means mountedupon the trailing portion of said platform structure and responsive todeformations induced upon said trailing portion upon the application ofa vehicle load thereto, said third electrical strain gage means and saidfourth electrical strain gage means being connected in a pair of arms ofsaid bridge circuit arrangement differing from that of the pair of armsof said first electrical strain gage means and said second electricalstrain gage means.
 4. Apparatus for sensing the direction of travel of avehicle as in claim 3, wherein said first electrical strain gage meansand said third electrical strain gage means are connected in oppositearms of said bridge circuit arrangement and wherein said secondelectrical strain gage means and said fourth electrical strain gagemeans are connected in a different pair of opposite arms of said bridgecircuit arrangement.
 5. Apparatus for sensing the direction of travel ofa vehicle as in claim 4, wherein said means connected to the output ofsaid bridge circuit arrangement is a DC differential amplifier, theoutput of said bridge circuit arrangement being taken across theterminal point joining said first electrical strain gage means and saidsecond electrical strain gage means and the terminal point joining saidthird electrical strain gage means and said fourth electrical straingage means.
 6. Apparatus for sensing the direction of travel of avehicle as in claim 5, wherein sAid first, second, third and fourthelectrical strain gage elements are of the tension or compressionresponsive type.
 7. Apparatus for sensing the direction of travel of avehicle as in claim 6, wherein said platform is of substantiallyrectangular shape and wherein said first, second, third, and fourthelectrical strain gage elements are each positioned near a differentcorner of said platform.
 8. Apparatus for sensing the direction oftravel of a vehicle as in claim 7, wherein the output of said DCdifferential amplifier will be zero when the vehicle load is at thecenter of said platform.
 9. Apparatus for sensing the direction oftravel of a vehicle as in claim 8, wherein said platform is a treadlescale used to measure the axle weight of a vehicle as it passesthereacross without error due to vehicle direction changes.